1. Field of the Invention
The present invention relates to a steering angle correcting system in a vehicle.
2. Description of the Related Art
Many concepts have been proposed hitherto for correcting the steering angle applied by a driver of a vehicle in accordance with a driving situation to provide an actual steering angle. For example, a concept for correcting the steering angle applied by a vehicle's driver in accordance with a yaw rate (an angular speed about a vertical line passing through a center of gravity of a vehicle) to provide an actual steering angle has been proposed in U.S. Pat. No. 3,871,468. A concept for correcting the proportion of an actual steering angle to an input steering angle in accordance with a vehicle speed has also been proposed in U.S. Pat. No. 4,310,063. These concepts are different from an automatic operative vehicle in that the driver basically drives the vehicle.
In recent years, marvelous progress in computer technology has accelerated the development of the technique regarding the mental capacity level for utilizing various sensors for grasping a situation ahead of the vehicle in advance and utilizing the outputs from the sensors. For example, the relative positional relationship of the subject vehicle relative to a lane ahead of the subject vehicle and the degree of curvature of the lane could be known, for example, from an image analysis of an image by a CCD camera. A radar technique is capable of detecting the presence of an obstacle ahead of the subject vehicle, quickly calculating a distance from the subject vehicle to the obstacle, and deducing a possibility of collision to warn a driver of the collision by means of an alarm, or to provide an automatic braking or to take an avoiding action.
An "automatic operative vehicle" which is automatically steered by utilizing an output from this type of "foreseeing sensor" still has room for improvement in cost and reliability, but is being brought into completion as a basic technology. This concept is different from the above concepts in that the driver is not basically a person who drives the vehicle. The present assignee has also previously proposed a technique relating to such concept in U.S. Pat. No. 5,350,912.
Before the technology of the automatic operative vehicle is improved and spread, it is surmised that a man-machine cooperation system utilizing, to the maximum, outputs from the foreseeing sensors with a human taking the leadership of driving is realized. Under the cooperation system, the human approves the operation of a computer by his own intention while receiving a control output from the computer based on the sensor information, when there is a contrariety between the operation of the computer and the human's intention, the human can immediately intervene into the contrariety to realize a driving according to the his own intention. The technology already put into practical use based on this type of concept includes an auto-cruising as a control technique limited to the travel speed of the vehicle, but there is still not a technique put into practical use with regard to the control of the lateral motion of the vehicle.
The feature of the technique utilizing the foreseeing sensor is in that a situation which will occur from now on is predicted, and a correction motion is applied as required based on the result of the prediction. In this case, the phase is fast and a smooth driving is feasible, as compared with a feedback technique detecting an already produced phenomenon to apply the correcting motion.
There is also a technique described in U.S. Pat. No. 5,350,912, in which a steering angle is input to a steering system based on information from the CCD camera to cause the vehicle to travel along a lane. In this patent, a steering section is shown in an illustrative embodiment, but it is not described that the steering section is fixed to a vehicle body in what manner. If the vehicle is a usual automatic operative vehicle, it is surmised as one method that the steering section is fixed and the steering system is driven directly. In a system in which the steering section is fixed to the vehicle body in the above manner, it is a matter of course that a reaction force during steering of the steering section is borne by the vehicle body.
It is believed that a steering wheel for steering by a human is of course mounted, although not being clearly shown in the known technique (U.S. Pat. No. 5,350,912). In this case, during automatic operation by the system, the steering wheel is moved at all times in a clockwise or counterclockwise direction in response to a control output, and if the driver desires to give his intention, an interruption steering can be achieved by directly turning the steering wheel.
When the interruption steering is conducted, the system acts against the driver's intention at the beginning and hence, it is undesirable that the steering force is heavy. When the driver applies the interruption, an inertial force of a driving motor and an internal friction force in a reducer placed for the purpose of increasing the motor output become resistances. The simplest technique for decreasing these resistances is to specially prepare a clutch for disconnecting the driving motor from the system by sensing the intervention of the human by any sensor. However, with regard to the sensor for sensing the intervention of the human and the disconnecting clutch, no small-sized and inexpensive sensor and clutch are yet developed technically.
When a steering mechanism drives the steering system directly, a rotative torque and rotational speed borne by the steering mechanism are necessarily increased in order to prevent the vehicle from departing from a lane. Consequently, the driving motor is large-sized, but in a usual design of the steering system, it may be very difficult in many cases to prepare a space for placement of such a large-sized device. If a technique in which a small energy need only be required to correct the steering angle can be proposed herein, it is possible to easily provide a steering angle correcting system without making a large change in layout of the existing steering system.